Troubleshooting sign-in and Webmail

User cannot sign in

Verify the exact login format, active state, temporary password, password policy and licence mode. Do not reset a password before confirming the correct account and domain.

Signs in but has no mailbox

Confirm that the mailbox exists, is linked to the user, is active and has accessible storage. In Proxy mode, verify the current context.

Cannot see a team mailbox

Review Mail Access Mode, the sharing or delegation entry, permissions and the mailbox domain. After a permission change, the user may need to sign out and sign in again.

Cannot send using an identity

Check identity ownership, Send As or On Behalf, default identity, licence SMTP state and module effective state. Do not grant a broad administrator role as a workaround.